On Thu, Apr 10, 2014 at 05:23:49PM +0800, Liu Ying wrote: > The i.MX pwm version2 is embedded in several i.MX SoCs, such > as i.MX27, i.MX51 and i.MX6SL. There are four 16bit sample > fifos in this IP, each of which determines the duty period > of a PWM waveform in one full cycle. The IP spec mentions > that we should not write a fourth sample because the fifo > will become full and trigger a fifo write error(FWE) which > will prevent the PWM from starting once it is enabled. In > order to avoid any sample fifo overflow issue, this patch > does software reset to clear all the sample fifos in the > very beginning of the pwm configuration function. > > The fifo overflow issue can be reproduced by the following > commands on the i.MX6SL evk platform, assuming we use pwm2 > for the debug LED which is driven by the pin HSIC_STROBE > and the maximal brightness is 255. > echo 0 > /sys/class/leds/user/brightness > echo 0 > /sys/class/leds/user/brightness > echo 0 > /sys/class/leds/user/brightness > echo 0 > /sys/class/leds/user/brightness > echo 255 > /sys/class/leds/user/brightness > Here, FWE happens(PWMSR register reads 0x58) and the LED > can not be lighten. > > Cc: Sascha Hauer <[email protected]> > Cc: Shawn Guo <[email protected]>
Acked-by: Shawn Guo <[email protected]> > Cc: Lothar Waßmann <[email protected]> > Cc: [email protected] > Cc: [email protected] > Signed-off-by: Liu Ying <[email protected]> -- To unsubscribe from this list: send the line "unsubscribe linux-pwm" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
